1. Field of the Invention
The present invention relates to: an organic film composition, especially an organic film composition for a resist underlayer film composition or for a flattening composition useful in a multilayer resist process for microprocessing in manufacturing of a semiconductor device and so on; a method for forming an organic film by using the composition; a resist patterning process by using the composition; and a heat-decomposable polymer used in them.
2. Description of the Related Art
As an LSI advances toward higher integration and higher processing speed, miniaturization of a pattern size is rapidly progressing. In accordance with this miniaturization move, the lithography technology therein has achieved formation of a miniaturized pattern by shifting the wavelength of a light source shorter and by proper selection of a resist composition for such a light source. The main stream of this is a positive photoresist composition used in a monolayer. In this monolayer positive photoresist composition, a resist mechanism is constructed such that a skeleton having an etching resistance to dry etching by a gas plasma of a chlorine type or a fluorine type is incorporated into a resist resin, and that an exposed part thereof is dissolved, so that a pattern may be formed by dissolving the exposed part, and then a substrate to be processed may be dry etched by using the remained resist pattern as an etching mask.
However, if miniaturization is pursued without changing a film thickness of the photoresist film to be used, or in other words, if the pattern width thereof is made further narrower, the resolution of the photoresist film is decreased. In addition, when the photoresist film is pattern-developed by a developing solution, a so-called aspect ratio thereof is so large that a phenomenon of the pattern fall occurs. In view of the above-mentioned, film thickness of the photoresist film has been made thinner in accordance with this miniaturization move.
On the other hand, for processing of a substrate to be processed, the method wherein this substrate is dry etched by using a photoresist film having a formed pattern as an etching mask has been usually used. However, practically there is no dry etching method having a complete selectivity between the photoresist film and the substrate to be processed; and thus, during processing of the substrate, the resist film is damaged whereby causing collapse of the resist film during the time of processing of the substrate so that the resist pattern cannot be transferred precisely to the substrate to be processed. Because of this, the resist composition has been required to have a further higher dry etching resistance in accordance with the move to a finer pattern. Also, because of the shift of the exposure light to a shorter wavelength, a resin used for the photoresist composition is required to have a smaller light absorbance at the wavelength of the exposure light, so that, in accordance with the move to i-beam, KrF, and ArF, the resin has been shifting to a novolak resin, polyhydroxystyrene, and a resin having an aliphatic polycyclic skeleton. Practically however, the etching rate under the dry etching condition mentioned above is increasing so that recent photoresist compositions having a high resolution tend to have rather a lower etching resistance.
In the situation as mentioned above, a substrate to be processed must be dry etched by using a photoresist film having a thinner thickness and a lower etching resistance than ever; and thus, securement of a material and a process in this patterning process has become imperative.
One means to solve the problems mentioned above is a multilayer resist method. In this method, a middle layer film having the etching selectivity different from that of a resist upper layer film, i.e., a photoresist film, is put between the resist upper layer film and a substrate to be processed; and after a pattern is formed on the resist upper layer film, this pattern is transferred to the middle layer film by using the pattern on the upper layer film as a dry etching mask, and then the pattern is transferred further to the substrate to be processed by dry etching by using the middle layer film as a dry etching mask.
One of the multilayer resist methods is a three-layer resist method in which a general resist composition used in a monolayer resist method can be used. For example, an organic film formed of a novolak resin and the like is formed on the substrate to be processed as the resist underlayer film, on it is formed a silicon-containing film as the resist middle layer film, and further on it is formed a usual organic photoresist film as the resist upper layer film. Because the organic resist upper layer film can have a good selectivity relative to the silicon-containing resist middle layer film in dry etching by a fluorine gas plasma, the resist pattern can be transferred to the silicon-containing resist middle layer film by using dry etching by the fluorine gas plasma. According to this method, even if a resist composition with which a pattern having a sufficient film thickness to directly work on the substrate to be processed is difficult to be formed is used, or a resist composition whose dry etching resistance is insufficient to work on the substrate is used, the pattern can be transferred to the silicon-containing film, and then, by transferring the pattern by dry etching using an oxygen gas plasma, the novolak film pattern having a sufficient dry etching resistance for processing can be obtained.
Many technologies as to the organic underlayer film as mentioned above have been in the public domain for example, Patent Document 1). In recent years, however, a need of excellent filling-up or flattening characteristics, in addition to the dry etching characteristics, is increasing. For example, if there is a very fine pattern structure such as a hole and a trench on the underlayment substrate to be processed, the filling-up characteristic to fill up inside the pattern by a film without a void became necessary. Further, if there is a difference in the levels on the underlayment substrate to be processed, or a dense pattern area and a scarce pattern area co-exist on the same wafer, surface of the film needs to be flattened by the underlayer film. By flattening the underlayer film surface, variance of the film thickness of the middle layer film and the photoresist to be formed thereupon can be suppressed; and as a result, a focus margin of the lithography and a margin in the subsequent process steps of the substrate to be processed can be enlarged.
As to the means to improve the filling-up and flattening characteristics of the underlayer film composition, addition of a liquid additive such as a polyether polyol has been proposed (Patent Document 2). However, the organic film formed by this method contains a large quantity of the polyether polyol unit which is poor in the etching resistance thereby decreasing the etching resistance significantly; and thus, this is not suitable as the underlayer film for the three-layer resist process. As discussed above, the resist underlayer film composition having both the sufficient etching resistance and the excellent filling-up and flattening characteristics, as well as a patterning process using this, is wanted.
In addition, use of the organic film composition having excellent filling-up and flattening characteristics is not limited to the underlayer film for the three-layer resist process, but it can be used widely as a flattening material in the manufacturing process of a semiconductor, for example, as a material to flatten the substrate in advance of patterning by nanoimprinting. Currently, the CMP process is generally used for global flattening in the manufacturing process of a semiconductor; but the CMP process is costly so that this material receives a high hope for the global flattening method that displaces the CMP process.